The Villavieja Formation, Colombia

The Villavieja Formation is uppermost portion of the Honda Group, a 1250
meter thick collection of Miocene rocks located along the Magdalena River
in the badlands of central Colombia. The lower portion of the Villavieja
is richest in fossils, being a collection of sandstones and gray and red
mudstones. The upper layers contain volcanic deposits, and fewer fossils.

Though the region today is semi-arid, dominated by thorn-scrub acacia and
woody cactus, Villavieja was a lowland tropical forest in the Miocene.
Fossilized trunks of Goupioxylon have been found which resemble
wood of the living Goupia, a lowland forest tree that may grow to
30 or 40 meters tall.

The Villavieja Formation has yielded large numbers of vertebrate fossils,
many of them nearly complete skeletons and many of them large and well
preserved. This locality has been tremendously important for the study of
vertebrate evolution, particularly large mammals. Firstly, Villavieja is
uniquely situated in space. Most of South America is tropical, but few
fossil sites have been found there. The tropical soils and climates are
usually poor for preserving fossils, since decomposition is often too
rapid. Villavieja thus shows us life is a tropical region, while most fossil
sites in South America come from further south in the cooler temperate zone.

Secondly, Villavieja is situated uniquely in time. In the Late
Miocene and Early Pliocene,
South America came into contact with Panama and the North American continent.
When that happened, many species of plants and animals
migrated north or south and a vast mixing of previously isolated species
occurred. The migration of animals is called the "Great Faunal Interchange"
and is a major event in the history of the Neotropics. Villavieja animals
show us what life was like in the path of this interchange just before the
event occurred, giving us an idea of what survived, and what did not.

Most of the species from Villavieja have been found nowhere else.
Because of this, it has often been
difficult to correlate rock strata with layers from other localities. In
the past, it was assumed that the diversity of South American vertebrates
was rather uniform across the continent at any one time, recognizable by
the presence of certain key species which could be found in large numbers.
Work at Villavieja has shown that this is not the case, but that the
northern tropical faunas are quite different from those of more temperate
Patagonia.

The first significant discoveries of
fossil vertebrates in this area was made by Brother Ariste Joseph in 1923.
During the 20s and 30s, oil survey expeditions encouraged by the Colombian
goverment turned up a number of additional new and unusual finds.
In 1944, R. A. Stirton of UCMP
took special interest in the region and obtained funding for an expedition.
Though his ship caught fire and sank near Acapulco, he managed to reach
Colombia and gather financial support from several oil companies for his
research.

It was on this expedition that the partial skull and skeleton
of the fossil monkey Cebupithecia was discovered, a fossil that
immediately turned these badlands into a respected and important fossil
locality. Fossil primates
are exceedingly rare, and even when fossil monkeys are found, it is often
merely teeth or a jaw. The La Venta site has yielded fossils assignable
to as many as ten genera, whereas most localities will have no more than three.
As a result of the richness of vertebrate fossils here, the Villavoeja
Formation is one of the best-known and best-studied ancient faunas in
South America, of any age.